In traveling-wire electrical discharge machining (TW-EDM), a thin, continuous wire-like elongate electrode is axially caused to travel or is transported from a supply reel to a wind-up (take-up) reel and a workpiece is disposed in juxtaposition with the traveling-wire electrode while electrical energy in the form of time-spaced electrical pulses is supplied across a machining gap formed between the traveling wire and the workpiece in the presence of a dielectric fluid to effect a series of electrical discharges to remove material from the workpiece. As material removal proceeds, the workpiece is displaced relative to the axially transported wire electrode in a prescribed path to produce a desired cutting pattern in the workpiece.
Conventional machines designed to excute the TW-EDM process are provided with a pair of support arms extending from a column mounted upright on a base of the machine, one of the support arms guiding the continuous wire electrode unwound from the supply reel into the machining region where the workpiece machining portion is located while the other guides the wire electrode having undergone the machining action continuously to the take-up reel. The axial transportation of the wire electrode is effected by controlled rotary drive comprising feed and brake roller arrangements which also act to stretch the moving wire guided between the support members under a sufficient tension to allow the wire electrode to travel smoothly and precisely in machining position relative to the workpiece. As a result, considerable bending as well as tensile stresses are applied to the wire guiding members.
Since the wire electrode is relatively thin, it is difficult to maintain the tension exerted thereon precisely constant. Thus a change in tension exerted on the wire electrode tends to cause variation in deflection stress on the arms carrying the support members which in turn deviates the latter from the predetermined machining positions relative to the workpiece. There consequently ensue errors in cutting path which seriously affect the machining accuracy and there arises a danger of short-circuiting between the wire electrode and the workpiece which can lead to the interruption of the cutting operation. This problem is even more significant with larger machine having longer support arms.